DME is a commercially valuable product. For example, DME serves as a building block for the production of numerous chemicals. DME may be used, for example, as a component of chemical reactions, as an additive in liquefied petroleum gas, and also as a clean-burning or diesel replacement fuel.
Methanol, as a raw material, may be produced from natural gas. DME may thus be produced from methane by first converting methane in natural gas into methanol. Natural gas typically contains about 60 to 100 mole percent methane, the balance being primarily heavier alkanes. Alkanes of increasing carbon number are normally present in decreasing amounts. Carbon dioxide, hydrogen sulfide, nitrogen, and other gases may also be present in relatively low concentrations. Natural gas is a common and economical feedstock for producing methanol, although other feedstocks may also be used.
A typical methanol synthesis reactor (for conversion of syngas to methanol) will convert only about 20% to 60% of the syngas fed to the reactor in a single pass. To obtain higher conversions, the unreacted syngas is typically separated from the product methanol and recycled back to the reactor or directed to a second reactor to produce additional methanol. Methanol synthesis reactors are disclosed in, for example, U.S. Pat. Nos. 4,968,722, 5,219,891, 5,449,696, 6,723,886, and 5,177,114 and GB 2092172A, each of which are incorporated herein by reference to the extent they are not contradictory to embodiments disclosed herein.
Methanol synthesis reactors are typically operated at relatively high temperatures and pressures, for example, from about 400° F. to about 600° F. and from about 1000 psig to about 1500 psig. The requirement of a high temperature and pressure adds costs to the process in terms of energy and capital expenditures. Savings on energy costs and capital costs associated with pre-heating and pressurizing the feed gases to the methanol reactor would be beneficial to the process. Due to the low conversion per pass and high recycle requirement, a significant cost is associated with compression and heating of recycle gases following separation of the methanol product from unreacted gases in the methanol synthesis reactor effluent.
Accordingly, there exists a need for a process for the production of dimethyl ethers from methanol synthesis reactor effluents that provides energy savings and greater efficiency over conventional processes.